The present invention generally relates to a high temperature process chamber and a method for using the chamber and more particularly, relates to a high temperature process chamber that has improved heat endurance and a method for improving the heat endurance a process chamber.
In the fabrication of semiconductor devices, dry chemical etching occurs when a chemical reaction takes place between a gas and a wafer surface, with or without a plasma, while the resulting volatile product is pumped away. The dry etching process is typically selective and non-directional. In a plasma-assisted chemical etching process, the major role of the plasma is to maintain a supply of reactive species in the form of free radicals and excited neutrals.
In plasma-assisted chemical etching, material is selectively removed by a reactive gas created near or within a glow discharge from an initially non-reactive gas mixture. In most plasma etching systems, the injected gas itself rarely reacts with the surface that has been etched while free radicals are believed to be the major reactant species. The gas mixture is selected to produce reactive species by molecular dissociation into radicals and excitation of neutrals in the plasma. Because of the absence of physical enhancement or ion bombardment, plasma-assisted chemical etching is essentially isotropic and very selective. The plasma assisted chemical etching is therefore widely used when isotropic etching is required or when dimensional control is not critical. The most common example of plasma assisted chemical etching is the removal of a photoresist layer in an oxygen plasma, sometimes referred to as a plasma ashing technique.
The plasma ashing technique is an isotropic etch process of an organic photoresist material in an oxygen glow discharge where atomic oxygen is produced together with electrons. The oxygen atoms then react with the organic material to form the volatile products of CO, CO2 and H2O. It has been found that since most of the underlying film materials are not attacked by an oxygen plasma, over etching is frequently used to ensure that all resist materials are removed without residues. For instance, a wafer that is coated with 1 xcexcm photoresist material can be processed between 5 and 10 minutes. The plasma ashing process can also be used for descumming of wafers, i.e. removal of residual layers of photoresist or other organic material following a resist developing and hard baking processes. Typically, the residues can be removed in a 1 minute exposure to an oxygen plasma.
The plasma ashing process reduces costs and potential hazards of a wet chemical etching. It has therefore become an important etching step to remove photoresist materials, particularly those which have become insoluble in wet solvents. For instance, when the photoresist material has been exposed to a flourine or a chlorine dry etch environment during a polysilicon or oxide etching or to high current ion implantation. After a hardened top layer of the photoresist has been removed, a plasma etching or wet chemical etching process can be used to remove the remainder of the photoresist material. A plasma ashing process can also be followed by a cleaning step to remove ions and heavy metals which are not volatilized by the oxygen plasma process.
A typical inductively coupled plasma etch chamber 10 is shown in FIG. 1. In the etch chamber 10, the plasma source is a transformer coupled plasma source which generates a high density, low pressure plasma 12 decoupled from the wafer 14. The plasma source allows an independent control of ion flux and ion energy. Plasma 12 is generated by a flat spiral coil, 16, i.e. an inductive coil separated from the plasma by a dielectric plate 18, or a dielectric window on top of the reactor chamber 20. The wafer 14 is positioned sufficiently away from the coil 16 so that it is not affected by the electromagnetic field generated by the coil 16. There is very little plasma density loss since plasma 12 is generated only a few mean-free-path away from the wafer surface. The plasma etcher 10 enables a high density plasma an high etch rates to be achieved. In the etcher 10, and inductive supply 22 and a bias supply 24 are used to generate the necessary plasma field. Multi-pole magnets 26 are used for surrounding plasma 12 generated. A wafer chuck 28 which moves up-and-down by shaft 32 is used to hold wafer 14 during the etching process. A ground 30 is provided to one end of the inductive coil 16.
In a typical inductively coupled RF plasma etcher 10, a source frequency of 13.5 MHZ and a substrate bias frequency of 13.5 MHZ are utilized. An ion density of approximately 0.5xcx9c2.0xc3x971012/m3, an electron temperature of 3.5xcx9c6.0 eV, and a chamber pressure of 1xcx9c25 mTorr are used.
In the plasma ashing chamber 10 of FIG. 1, the wafer stage 28 operates at a typical high temperature of about 250xc2x0 C. in a photoresist stripping process. A lift cylinder 34 is installed under the support 36, as shown in FIGS. 2A, 2B, 3A and 3B. The support 36 is fastened to a bottom chamber wall 38, as shown in FIG. 3B by a plurality of screws 40. The lift cylinder 34 is operated by compressed airfed through an inlet needle valve 42 and an outlet needle valve 44. The shaft 32 is further supported and guided by a support cylinder 46. An upper support cylinder 48, as shown in FIG. 3A, is used to support and guide the shaft 32 located inside the plasma process chamber when the support 36 is fastened to the bottom chamber wall 38 of the plasma process chamber 10.
In the conventional plasma ashing chamber 10, the lift cylinder 34 which is operated by the needle valves 42,44 is mounted directly to the support 36 in close proximity of the plasma process chamber 10, i.e. by mounting directly to the bottom process chamber wall 38. Since the wafer stage 28 in the plasma process chamber 10 is kept at 250xc2x0 C. during a photoresist stripping process, the lift cylinder 34 operates at a temperature of about 70xc2x0 C. from the heat conduction through the support 36 and the support cylinder 46. Commercially available lift cylinders are not designed to operate at such high temperature and furthermore, are not equipped with anti-friction O-ring to function properly on a long term basis. The control elements, such as the needle valves 42,44 are also likely to fail when exposed to such high operating temperature. It has been found that there is a 65% failure rate of the lift cylinder during a four year running period on a plasma process chamber.
Numerous equipment problems have therefore been encountered in the conventional plasma process chamber 10. These include a loss of accurate speed control of the wafer stage 28 by the lift cylinder 34 due to failure in the needle valves 42,44. When the needle valves 42,44 are worn after extended exposure to high operating temperature, the control of compressed air flow through the needle valves 42,44 is no longer accurate and frequently results in too fast a speed in the upward movement of the wafer stage 28. Furthermore, after a failure in the lift cylinder 34 has occurred, the plasma process chamber must be opened in order to change the lift cylinder. During a preventive maintenance procedure, the temperature of the plasma process chamber must also be dropped to room temperature in order to carry out the procedure. When the operation of the chamber is resumed, the O-ring on the left cylinder does not seal properly since the seal has not expanded to its supposed volume at 70xc2x0 C. resulting in leaks through the seal. The conventional lift cylinder can only function properly for about six months which is impossible in maintaining a high throughput in the fabrication process.
It is therefore an object of the present invention to provide a high temperature process chamber that does not have the drawbacks or shortcomings of the conventional high temperature process chambers.
It is another object of the present invention to provide a high temperature process chamber that has improved heat endurance by insulating components of the chamber from the high temperature environment in the chamber.
It is a further object of the present invention to provide a high temperature process chamber that has improved heat endurance when the process chamber operates at a temperature of at least 200xc2x0 C.
It is another further object of the present invention to provide a high temperature process chamber that has improved heat endurance by connecting a heat insulating adapter between the chamber body and a lift cylinder used for lifting a wafer stage.
It is still another object of the present invention to provide a high temperature process chamber that has improved heat endurance by insulating a lift cylinder from the chamber such that the cylinder operates at a temperature below 40xc2x0 C.
It is yet another object of the present invention to provide a reactive ion etch chamber that is equipped with a wafer pedestal wherein a heat insulating adapter is used between the chamber body and a lift cylinder for preventing overheating of the lift cylinder.
It is still another further object of the present invention to provide a reactive ion etching chamber that is equipped with a wafer pedestal that operates at a temperature of at least 200xc2x0 C. by insulating a lift cylinder from the chamber such that the cylinder operates at a temperature not higher than 40xc2x0 C.
It is yet another further object of the present invention to provide a method for improving heat endurance of a process chamber by connecting a heat insulating adapter between a wafer pedestal that operating at 250xc2x0 C. and a lift cylinder that operates at a temperature below 40xc2x0 C. to avoid damaging the lift cylinder.
In accordance with the present invention, a high temperature process chamber that has improved heat endurance and a method for improving heat endurance of a process chamber are provided.
In a preferred embodiment, a high temperature process chamber that has improved heat endurance is provided which includes a chamber body equipped with a wafer pedestal for holding a wafer thereon and for processing the wafer at a temperature of at least 200xc2x0 C., a lift cylinder position below and outside the chamber body for operating the wafer pedestal in an up-and-down motion, the cylinder further includes components that are operable at temperatures lower than 40xc2x0 C., and an adapter means situated in between the wafer pedestal and the lift cylinder formed at least partially of a heat insulating material such that the high temperature of the wafer pedestal is substantially attenuated from the lift cylinder to allow the lift cylinder to operate at a temperature below 40xc2x0 C.
In the high temperature process chamber that has improved heat endurance, the lift cylinder is operated by pressurized air that is controlled by an input needle valve and an output needle valve. The high temperature process chamber is a reactive ion etch chamber, or a reactive ion etch chamber for stripping a photoresist layer, or a reactive ion etch chamber for stripping a photoresist layer operated at a temperature of about 250xc2x0 C. The adapter means may further include heat dissipating means, or heat dissipating means of a metal disc that has apertures therethrough. The adapter means may further include an insulator plate formed of a heat insulating material mounted to a bottom end of the adapter means for direct contact with the lift cylinder. The adapter means may further include an apertured collar, an apertured shaft and a locking pin for separating the adapter means into an upper portion and a lower portion, the upper portion is bolted to the chamber body and the lower portion is bolted to the lift cylinder. The adapter means is substantially fabricated of stainless steel. The lift cylinder may be substantially attenuated from the wafer pedestal to allow the cylinder to operate at a temperature below 40xc2x0 C.
The present invention is further directed to a reactive ion etch chamber that is equipped with a wafer pedestal which includes a chamber enclosure for conducting etching on a wafer positioned on a wafer pedestal at a temperature of at least 200xc2x0 C., a lift cylinder for elevating/lowering the wafer pedestal, the lift cylinder may be positioned outside the chamber enclosure, and a heat insulating adapter for connecting to the chamber enclosure at an upper end and to the lift cylinder at a lower end such that the lift cylinder operates at a temperature not higher than 40xc2x0 C.
In the reactive ion etching chamber that is equipped with a wafer pedestal, the lift cylinder consists of an upper portion and a lower portion connected by a quick disconnect means. The adapter may further include at least one apertured heat dissipating disc and at least one insulator plate made of a heat insulating material.
The present invention is further directed to a method for improving heat endurance of a process chamber which can be carried out by the operating steps of providing a process chamber that is equipped with a wafer pedestal therein, providing a lift cylinder situated outside of the process chamber for elevating/lowering the wafer pedestal, connecting a heat insulating adapter between the wafer pedestal and the lift cylinder, and conducting a process at a temperature of at least 200xc2x0 C. in the process chamber while maintaining a temperature of the lift cylinder at below 40xc2x0 C.
The method for improving heat endurance of a process chamber may further include the step of providing the process chamber in a reactive ion etch chamber. The method may further include the step of providing the heat insulating adapter equipped with at least one heat dissipating disc and at least one heat insulating plate. The method may further include the step of connecting the heat insulating adapter to the wafer pedestal in the lift cylinder by bolts. The method may further include the step of conducting a reactive ion etching process on a photoresist layer at a temperature of at least 230xc2x0 C., or the step of maintaining a temperature of the lift cylinder at below 40xc2x0 C.